Characterization of Botryosphaeriaceae and Cryphonectriaceae associated with Terminalia SPP. in Africa

Abstract:

Fungal diseases of trees are serious impediments to forest expansion and productivity. While the adverse effects of diseases of non-native plantation forest trees are increasingly recognized in Africa, the health of native trees has been virtually ignored. This is especially acute as many commercially propagated trees are related to native woody plants and recurrent movement of pathogens between native and non-native trees is increasingly being recorded. The genus Terminalia accommodates important indigenous tree species in Africa that provide a variety of valuable wood and non-wood products. Despite the importance of Terminalia spp., very little information has been recorded on their health problems. Research for this dissertation aimed at studying some of the fungal diseases of native and non-native Terminalia species in Africa. Special reference was provided to fungi in the Botryosphaeriaceae, a group of pathogens that infect host plants without always producing clear symptoms. A literature review, presented in Chapter One, highlighted the limited information available on the pathogens and pests associated with these trees. Most disease reports include minimal detail. Often the causal agents had been identified based only on morphology and were not classified to the species level. Studies performed in chapter two compared the assemblages of endophytic species of the Botryosphaeriaceae from T. catappa in Cameroon, South Africa and Madagascar. Five species were identified and two of these are new to science and provided with the names N. batangarum and L. mahajangana. The assemblage of the Botryosphaeriaceae varied from one country to another, however, colonization patterns in the three areas were similar. Greenhouse inoculation trials performed on young T. catappa trees showed variation among isolates tested, with L. pseudotheobromae being the most pathogenic. Chapter three represents the first investigation of the Botryosphaeriaceae on native Terminalia trees in Cameroon and Africa. Morphological and DNA sequence data were used to identify these species as L. theobromae, L. pseudotheobromae, L. parva and E. endophytica. Pathogenicity trials performed on young T. mantaly and T. catappa trees revealed that L. pseudotheobromae was the most virulent species. In chapter four, species of Botryosphaeriaceae on native Terminalia spp. in Southern Africa were studied. Nine species were identified from T. sericea and T. sambesiaca. Seven of these, L. crassispora, L. pseudotheobromae, D. alatafructa, P. olivaceum, N. parvum, N. kwambonambiense and N. vitifusiforme represented previously described species and two, L. cryptotheobromae and N. terminaliae, were described as new. The genetic analyses of populations of L. theobromae and L. pseudotheobromae presented in chapter five showed clear genetic divergence between L. theobromae and L. pseudotheobromae supporting their distinction as separate species. Both L. theobromae and L. pseudotheobromae populations possessed high gene diversity, moderate degrees of genotypic diversity, and high levels of gene flow between isolates from T. cacao and Terminalia spp. Both sexual and asexual modes of reproduction were found. The last chapter of this dissertation presents the description of a new genus in the Cryphonectriaceae, Aurifilum marmelostoma, using a combination of molecular and morphological tools. This fungus is the second genus in this family described from Terminalia spp. Pathogenicity tests conducted to assess its ability to cause disease revealed that the fungus is a possible pathogen of this tree. An extensive number of potentially pathogenic fungi, including five new species were found associated with native and non-native Terminalia spp. in Africa. As some of these fungal species could serve as sources of inoculum onto economically important crops, research presented in this dissertation provides a foundation for understanding health issues affecting Terminalia and related genera in selected regions in Africa. Hopefully, results of this study will serve as valuable tools in forestry management in Africa. Copyright